Electrolytic rectifier



M y 1933. R. D. MERSHON ELECTROLYTIC RECTIFIER Filed Nov. 1930 i i 4 7 I1005 (190 Q t Patented May 9, 1933 PATENT OFFICE RALPH D. MERSHON, OFNEW YORK, N. Y.

ELECTROLYTIC nnc'rrrma Application fled November 18, 1980. Serial. No.496,441.

' This invention relates to electrolytic rectifiers, for convertingalternating voltage and current into direct. As is well known, suchdevices depend for their operation upon the film which may be formedupon the surface of certain metals and which possesses the peculiarproperty of offering low resistance to the flow of current from theelectrolyte to the metal but relatively high resistance to currenttending to flow from the metal to the electrolyte. If, when, anelectrode having such a film and an electrode of non-filming metal orother conducting material are immersed in a suitable electrolyte and thetwo are connected to a source of alternating current only the currentimpulses which are positive with respect to the filmed electrode will besuppressed and those which are positive with respect to the non-filmingelectrode will pass through the f Hence the current from the filmed rodewill be unidirectional, though more or less pulsating in character. Iftwo filmed Q electrodes are used both current impulses of each cycle maybe rectified.

By reason of their simplicity and relatively low cost'such devicesofi'er attractive bilities, but these possibilities have been ddifiicult to realize in practice. In the st place, when the filmedelectrodes are made of pure metal (or metal containing nothing else butthe impurities found in commercial grades, which impurities are lallysilicon, titanium and iron, sometimes opper also), the efliciency of therectifier is tow, especially when the electrolyte is hot, it isaptto beby reason of the losses due to the resistance encountered by thecurrent. Also, the filmedmetal is subject to rapid corrosion due to there eated break-down and re-formation of the film incident to therectifying action. These drawbacks are to a considerable extent overcomeby making 1e filmed electrodes of an alloy of alumium, magnesiumandcopper, as described and claimed in my co ending application 9 ialNo. 317,610, file November 6, 1928, t in the course of continuedinvestigation ave found that aluminum alloyed with calcium, andpreferably containing nickel also, is still better, as evidenced bylonger life and by high efliciency even at boiling temperature.Advantageous results can be obtained with less, but I prefer to use atleast about three per cent of calcium and two per cent of nickel. A likeamount of copper may be used, but I consider nickel better. Of thelatter element I may use as much as six per cent, and in some casesmore, but I have not observed that the results are any better than withabout 4 per cent. As for the calcium content I have not found that morethan ten per cent offers any material advantage, but the invention isnot limited to that amount since the alloy may contain calcium up to themaximum that can be alloyed with aluminum or with aluminum and nickel.Eight per cent of calcium is a good average amount, being satisfactoryfor impressed voltages exceeding 200 volts (R. M. S.) as well as forlower. Using an alloy composed of aluminum 88 per cent, calcium. 8 percent, and nickel 4 per cent, approximately, with a condenser in parallelwith the D. G. terminals of the rectifier, I have obtained an efiiciencyof 69 per cent over long periods of time, even with the electrolyteboiling. At first the efiiciency may be ashigh as 88 per cent or higher.Instead of nickel I may use other meta s such as copper, cobalt, orsilicon, but the electrical results are less advantageous. In general Imay use any one or more of the metals nickel, copper, cobalt andsilicon.

My experience indicates that an acid electrolyte, say one containingborax or sodium phosphate and boric or phosphoric acid givessubstantially better results in the long run than a neutral or alkalineelectrolyte, say one containing only borax or sodium hosphate orsodiumhydroxid. I prefer, owever, a solution containing one-half poundof anhydrous sodium tetraborate and one and a half pounds of boric acidper gallon of water. 95

For thenon-filming electrode carbon may be used, or any non-filmingmetal, preferably one which is not readlly deposited on the filmingelectrodes, as for example highsilicon iron, but I prefer graphite, asit resists well the chemical or electrochemical attack incident to theoperation of the rectifier. The metal tank or vessel containing theelectrol te may be used as the non-filmi electro e, as is common in theart.

11 the accompanying drawing,

1. 2, 3, 4 and 5 illustrate diagrammatically various formsofelectrolytic rectifiers 'in'which my invention may be embodied.

Throughout the drawing, is a tank or vessel for the electrolyte, 11, 11are filmed electrodes of aluminum-calcium-nickel alloy, 12 is anon-filming electrode of graphite, T is an auto-transformer or balancecoil R, R are the terminals for the rectified output, one connected tothe neutral point of the balance coil and the other to the anode, oranodes 12. A, A" are the input terminals for connection with a source ofalternating voltage and current.

.. and onlythose which are imp needed. When both filmed In Fig. 1 therectifier has one filming electrode and is therefore of the half-wavetype, that is, (positive impulses impressed upon the filme electrode 11are su presigd on e non-filming electrode 12 are passed. In Fi 2 and 3two cells such as are shown in h ig. 1 are used for full-waverectification, .111 the one case with the filmed electrodes connected tothe transformer or bal' ance coil and in. the other with thenonelectrodes connected thereto. In Fig. 4 1 th filmedelectrodee are inthe same vessel andonly one non-filming electrode is e ectrodes. areinfthe same tank a balance .coil or transformer is necesesary, as ,inFig. 4, for exand also in the arrangements shown in 2 and 3, in whichonly two halfwave cells are .used. With four or .more

such cells they may be connected as in Fig. 5,. in which case no balancecoil or transformer is needed, though a transformer may helempl'oyed-asa convenient means for step- M p alternating voltage up assume' in or oThe operation will be readily by tracin the course of the current in anof the gures. For e xample, ,ig. a an impulse coming in from A. Unableto pass through the termmpl thrgg t'cgnductoil' 13 to terminzll R,ltihenc; thr 1 e' trans atmg' evice not s own to terminals R, and fromthe lattenterininal to the non-film' electrode 12, the electrolyte,filmed. electro e 11, and thenceto the transformer T and out throughterminal A. When the alternating. volta reverses the flow is fromterminal A thro conductor 18, terminals R, B, unfilmed electrode 12 andfilmed electrode 11 to terminal A. In Fig. ,5 an impulse comiig in atterminal A (me through unfilm electrode electrode 11' the current flows12 in the lower tank at the right, filmed electrode 11 in the same tank,conductor 1 terminals R, R, conductor 15, unfilm electrode 12 in theupper tank at the left filmed electrode 11 in the same tank, an thenceto terminal A. When the alternating volta e reverses, the current flowsfirst through t e lower cell at the leftand out through the upper cellatjhe r' It is to be understood that e invention is not limited to thespecific details herein described but can be carried out in other walyswithout departure from its spirit.

claim- 1. An electrolytic rectifier having an electrode made of analuminum-calcium allo 2. An electrolytic rectifier having an 0 cctrodemade of an aluminum-calcium alloy containin nickel.

3. An e ectrolytic rectifier having an electrode made of analuminum-calcium alloy containin copper.

4. An e ectro ytic rectifier having an electrode made of analuminum-calcium alloy having a calcium content not less than about 3per cent.

5. An electrol ic rectifier having an electrode made 0 analuminum-calcium alloy having a calcium content from 8 per cent to 10per cent, a proximately.

6. An electro 'c rectifier having an electrode made 0 analuminum-calcium allo containing not less than about 2 per cent 0nickel.

7. An electrolytic rectifier having an electrode made of analuminum-calcium alloy containing from about 2 percent to 6 r cent ofnickel.

8. An electrolytic rectifier ha i" an electrode made of aluminum-calciumhaving a calcium content of from 8 to 10 per cent, approximately, andcontaining from about 2 to 6 per cent of nickel.

9. An electrol 'c rectifier hav' .an electrode made of uminum-calcium oyhaving a calcium content of about 8 cent and containing about 4 per cent0 nickel.

10. An electrolytic rectifier havi an electrode made of aluminum-calciumy containing at least one other metal of the class consisting of nickel,cobalt, copper and sili- 11. An electrolytic rectifier com ri a filmedelectrode composed of alumi huh i ab cium alloy, a non-filmin electrode,and an electrolyte in which sai electrodes are immersed, containing anacid of the clan of boric and phosphoric acids.

12. An electrolytic rectifier com a filmed electrode com ofaluminumcalcium alloy, a nong electrode, and an electrolyte which saidelectrodes are immersed, containing born: and boric acid in solution.

13. An electrode for an electrolytic recti- 1,ooa,oso 3 10 signature.

RALPH D. MERSHON.

